Biometric authentication

ABSTRACT

A method for authenticating a user of an electronic device is disclosed. The method comprises: responsive to detection of a trigger event indicative of a user interaction with the electronic device, generating an audio probe signal to play through an audio transducer of the electronic device; receiving a first audio signal comprising a response of the user&#39;s ear to the audio probe signal; receiving a second audio signal comprising speech of the user; and applying an ear biometric algorithm to the first audio signal and a voice biometric algorithm to the second audio signal to authenticate the user as an authorised user.

TECHNICAL FIELD

Embodiments of the disclosure relate to biometric authentication, andparticularly to methods, apparatus and computer-readable mediums forauthenticating a user based on ear biometric data.

BACKGROUND

It is known that the acoustic properties of a user's ear, whether theouter parts (known as the pinna or auricle), the ear canal or both,differ substantially between individuals and can therefore be used as abiometric to identify the user. One or more loudspeakers or similartransducers positioned close to or within the ear generate a stimulus,and one or more microphones similarly positioned close to or within theear detect the response of the ear to the stimulus. One or more featuresmay be extracted from the response signal, and used to characterize anindividual.

For example, the ear canal is a resonant system, and therefore onefeature which may be extracted from the response signal is the resonantfrequency of the ear canal. If the measured resonant frequency (i.e. inthe response signal) differs from a stored resonant frequency for theuser, a biometric algorithm coupled to receive and analyse the responsesignal may return a negative result. Other features of the responsesignal may be similarly extracted and used to characterize theindividual. For example, the features may comprise one or more melfrequency cepstrum coefficients. More generally, the transfer functionbetween the stimulus and the measured response signal (or features ofthe transfer function) may be determined, and compared to a storedtransfer function (or stored features of the transfer function) which ischaracteristic of the user.

Other acoustic properties of a user's ear include otoacoustic emissions,whether spontaneous (i.e., generated by the ear without externalstimulation) or evoked (i.e., generated by the ear in response to astimulus signal such as one or more pure tones, a tone burst, etc.).Such otoacoustic emissions may also differ between individuals and cantherefore be used to discriminate between individuals or to identify aparticular individual.

One problem faced by biometric algorithms is the need to achieveacceptable performance in two respects. First, the algorithm shouldprovide acceptable security so that unauthorised users are not falselyrecognized as authorised users. The likelihood that the algorithm willaccept an access attempt by an unauthorised user is known as the falseacceptance rate (FAR), and should be kept low if the algorithm is toprovide reasonable security. Second, the algorithm should work reliably,so that authorised users are not falsely rejected as unauthorised. Thelikelihood that the algorithm will reject an access attempt by anauthorised user is known as the false rejection rate (FRR), and shouldalso be kept low if the algorithm is not to prove frustrating forauthorised users seeking authentication.

The problem is that these two performance requirements conflict witheach other. A low FRR can be achieved by relaxing the requirements for auser to achieve authentication. However, this will also have theconsequence of increasing the FAR. Conversely, a low FAR can be achievedby making the requirements for a user to achieve authenticationstricter. However, this will have the consequence of increasing the FRR.

One way to decrease both FAR and FRR is to increase the efficacy of thebiometric algorithm itself. However, designing the algorithm to achievehigh performance is difficult. Further, the efficacy may depend onfactors which are outside the designers' control. For example, theefficacy of the algorithm may depend on the quality of the biometricdata (e.g., noise levels, etc.), or the discriminatory nature of thebiometric itself.

One known technique for improving the efficacy of the authentication isto combine (or “fuse”) multiple authentication processes together,whether biometric or not. For example, a user may be required to input asecurity password or pin number in addition to providing a voice input(e.g., for voice biometric authentication). The authentication processesmay be combined using score-level fusion, or result-level fusion. In theformer case, separate scores are obtained for each authenticationprocess indicating the likelihood that a user is an authorised user.Those scores are then combined and compared to a threshold to determinewhether the user should be authenticated as the authorised user. In thelatter case, separate results are obtained for each authenticationprocess (e.g., through separate comparison of each score to acorresponding threshold) and then combined. For example, a user may beauthenticated only if the individual authentication results are allpositive. By fusing multiple authentication processes in this way, theFAR and FRR values for the combined authentication process can be muchlower than the FAR and FRR values associated with an individualauthentication process.

However, it can be time consuming and inconvenient to provide multipleinputs as part of an authentication process. Users typically wantauthentication to be both reliable and secure, while taking as littletime as possible. Preferably, the authentication process should even beinvisible to the user, such that they are authenticated without evenrealising that an authentication process has taken place.

SUMMARY

Embodiments of the present disclosure seek to address these and otherproblems.

For example, in one aspect the present disclosure provides a method forauthenticating a user of an electronic device. The method comprises:responsive to detection of a trigger event indicative of a userinteraction with the electronic device, generating an audio probe signalto play through an audio transducer of the electronic device; receivinga first audio signal comprising a response of the user's ear to theaudio probe signal; receiving a second audio signal comprising speech ofthe user; and applying an ear biometric algorithm to the first audiosignal and a voice biometric algorithm to the second audio signal toauthenticate the user as an authorised user.

In one embodiment, the trigger event comprises a predetermined keywordspoken by the user. In such an embodiment, the method may furthercomprise additionally applying the voice biometric algorithm to thepredetermined keyword (which may also be comprised within the secondaudio signal) to authenticate the user as an authorised user.

Another aspect of the disclosure provides an authentication device forauthenticating a user of an electronic device. The authentication devicecomprises: an audio signal generation module for generating, responsiveto detection of a trigger event indicative of a user interaction withthe electronic device, an audio probe signal to play through an audiotransducer of the electronic device; one or more inputs for receiving afirst audio signal comprising a response of the user's ear to the audioprobe signal, and a second audio signal comprising speech of the user;and a biometric authentication module for utilizing an ear biometricalgorithm on the first audio signal and a voice biometric algorithm onthe second audio signal to authenticate the user as an authorised user.

In one embodiment, the trigger event comprises a predetermined keywordspoken by the user. In such an embodiment, the biometric authenticationmodule is further for utilizing the voice biometric algorithm on thepredetermined keyword to authenticate the user as an authorised user.

A further aspect of the disclosure provides an electronic devicecomprising an authentication device as set out above. The electronicdevice may be portable and/or battery powered, such as a smartphone, anaudio player, a mobile or cellular phone, or a handset.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of examples of the present disclosure, and toshow more clearly how the examples may be carried into effect, referencewill now be made, by way of example only, to the following drawings inwhich:

FIG. 1a shows a personal audio device according to one configuration;

FIG. 1b shows a personal audio device according to anotherconfiguration;

FIG. 2 is a flowchart of a method according to embodiments of thedisclosure;

FIG. 3 is a flowchart of a method according to further embodiments ofthe disclosure; and

FIG. 4 is a schematic diagram of a biometric authentication systemaccording to embodiments of the disclosure.

DETAILED DESCRIPTION

As noted above, ear biometric data may be acquired by the generation ofan acoustic stimulus (which may be audible or non-audible, e.g.,ultrasonic), and the detection of an acoustic response of the ear to theacoustic stimulus. One or more features may be extracted from theresponse signal, and used to characterize the individual. The acousticresponse of the ear may relate to the acoustic transfer function of theear, and/or otoacoustic emissions from the ear. Alternatively oradditionally, otoacoustic emissions may be spontaneous, and detectedwithout any requirement for an acoustic stimulus.

Ear biometric data may be acquired using a personal audio device. Asused herein, the term “personal audio device” is any electronic devicewhich is suitable for, or configurable to, provide audio playbacksubstantially to only a single user. Some examples of suitable personalaudio devices are shown in FIGS. 1a and 1 b.

FIG. 1a shows the application of an electronic device arrangement 100 toa user's ear, with the arrangement 100 comprising a personal audiodevice 150 (in the illustrated embodiment, an in-ear headphone orearphone, insert headphone, or ear bud) and a host device 160 (in theillustrated embodiment, a smartphone). In such an embodiment, thefunctionality discussed below may be provided solely in the personalaudio device 150, solely in the host device 160, or split between bothdevices (i.e. with each device performing different aspects). FIG. 1bshows the application of a personal audio device 170 (in the illustratedembodiment, a smartphone) to a user's ear. In this example, therefore,there is no separate host device and the functionality discussed belowis carried out in the personal audio device itself.

FIG. 1a shows a schematic diagram of a user's ear, comprising the(external) pinna or auricle 112 a, and the (internal) ear canal 112 b.An electronic device arrangement 100 comprises a personal audio device150 and a host device 160.

As noted above, in the illustrated embodiment the personal audio device150 comprises an in-ear headphone (or earphone), insert headphone, orear bud. This headphone is configured to be partially or totallyinserted within the ear canal 112 b, and may provide a relatively tightseal between the ear canal 112 b and the external environment (i.e., itmay be acoustically closed or sealed). Alternative personal audiodevices include circum-aural headphones (e.g., those headphonescomprising a shell which substantially surrounds and encloses theauricle), supra-aural headphones (e.g., those headphones which do notsurround or enclose the user's ear, but rather sit on the auricle 112a), intra-concha headphones or earphones (e.g., those headphones whichsit inside the user's concha cavity), and smartphones or mobile phonesetc. (see FIG. 1b ).

The personal audio device 150 comprises one or more loudspeakers 152 andone or more microphones 154. The one or more loudspeakers 152 arepositioned on an internal surface of the headphone, and arranged togenerate acoustic signals (e.g., audible or inaudible signals, such asultrasonic waves) towards the user's ear and particularly the ear canal112 b. The one or more microphones 154 (hereinafter, “ear microphones”)are also positioned on the internal surface of the headphone, andarranged to detect acoustic signals within the internal volume definedby the headphone (in the illustrated embodiment, the ear canal 112 b).

The headphone may be able to perform active noise cancellation, toreduce the amount of noise experienced by the user of the headphone.Active noise cancellation operates by detecting a noise (i.e. with amicrophone), and generating a signal (i.e. with a loudspeaker) that hasthe same amplitude as the noise signal but is opposite in phase. Thegenerated signal thus interferes destructively with the noise and solessens the noise experienced by the user. Active noise cancellation mayoperate on the basis of feedback signals, feedforward signals, or acombination of both. Feedforward active noise cancellation utilizes oneor more microphones on an external surface of the headphone, operativeto detect the environmental noise before it reaches the user's ear. Thedetected noise is processed quickly, and the cancellation signalgenerated so as to match the incoming noise as it arrives at the user'sear. Feedback active noise cancellation utilizes one or more errormicrophones positioned on the internal surface of the headphone,operative to detect the combination of the noise and the audio playbacksignal generated by the one or more loudspeakers. This combination isused in a feedback loop, together with knowledge of the audio playbacksignal, to adjust the cancelling signal generated by the loudspeaker andso reduce the noise. The ear microphone 154 shown in FIG. 1a maytherefore form part of an active noise cancellation system, for example,as an error microphone.

The personal audio device 150 may comprise a further microphone 156positioned such that, in use, the microphone 156 lies close to theuser's mouth and therefore primarily detects the user's voice. Themicrophone 156 may be termed the voice microphone herein. In theillustrated embodiment, the voice microphone 156 is provided within thewired connection to the host device 160. In other embodiments, the voicemicrophone 156 may be provided on the end of an arm as part of aheadset, for example.

The personal audio device 150 and the host device 160 may be operativelycoupled together, such that signals and/or data can be passed betweenthem. For example, signals detected by the microphones 154, 156 may bepassed from the personal audio device 150 to the host device 160; audiosignals to be played back to the user may be passed from the host device160 to the personal audio device. In some embodiments, biometricauthentication results may be passed between the personal audio device150 and the host device 160.

In the illustrated embodiment, the personal audio device 150 is coupledto the host device 160 via a wired connection. Those skilled in the artwill appreciate of course that any operative connection between the twodevices may be provided, such as a wireless connection (e.g.,Bluetooth®).

FIG. 1b shows an alternative personal audio device 170, which is amobile or cellular phone or handset. The handset 170 comprises one ormore loudspeakers 172 for audio playback to the user, one or more earmicrophones 174 which are similarly positioned to detect acousticsignals in the vicinity of the user's ear, and one or more voicemicrophones 176 to detect the user's voice.

In use, the handset 170 is held close to the user's ear so as to provideaudio playback (e.g. during a call). While a tight acoustic seal is notachieved between the handset 170 and the user's ear, the handset 170 istypically held close enough that an acoustic stimulus applied to the earvia the one or more loudspeakers 172 generates a response from the earwhich can be detected by the one or more ear microphones 174. As withthe other devices, the loudspeaker(s) 172 and ear microphone(s) 174 mayform part of an active noise cancellation system.

FIG. 2 is a flowchart of a method for authenticating a user as anauthorised user of an electronic device. The method may utilize any ofthe personal audio devices discussed above with respect to FIGS. 1a and1 b, for example, and may be performed by an authentication device whichis arranged exclusively within the personal audio device, exclusivelywithin a host device coupled to that personal audio device, or which isdistributed between the host device and the personal audio device.

In step 200, the authentication device monitors for an event whichtriggers the authentication process (hereinafter, “trigger event”).Various events are contemplated as trigger events according toembodiments of the disclosure.

In one embodiment, the trigger event is indicative of a user interactionwith the authentication device. The trigger event may alternatively oradditionally be indicative of a user's desire to interact with thepersonal audio device using speech. For example, the trigger event maybe associated with activation of a virtual assistant, e.g., Siri,Cortana, Alexa (all ®), etc.

The trigger event may comprise actuation of a physical or virtual buttonon the personal audio device. Personal audio devices often have suchbuttons in order to send control signals to the personal audio deviceand/or a host device. Different control signals may be generated basedon the type of button actuation (e.g., a short or long press) or on asequence of multiple button actuations (e.g., a chain of two or threebutton presses in sequence). The button may physically move in responseto the user interaction (e.g., a physical button), or comprise acapacitive or ultrasonic sensor (e.g., a virtual button). In anotherexample, a personal audio device may detect finger taps or other userinteractions with the device via a microphone (such as the earmicrophones 154, 174 and/or the voice microphones 156, 176). Pulses ofaudio detected by the microphone may be determined as being indicativeof a tap of the user's fingers on the microphone. In this way, themicrophone itself functions as a button. Trigger events in which abutton is actuated (or its functional equivalent) consume small amountsof power.

In another example, the user interaction may be a spoken interaction.For example, the user may speak a predetermined word or phrase (“triggerphrase”), such as “Hey Siri”, “OK Google”, etc., which is detected by atrigger phrase detect module in the authentication device.

In step 202, it is determined whether a trigger event has been detected.If no trigger event has been detected, the method returns to step 200and the authentication device continues to monitor for a trigger event.If a trigger event is detected, the authentication process is initiatedand the method proceeds to step 204.

In step 204, the authentication device generates an audio probe signalto be played through an audio transducer of the personal audio device inthe vicinity of the user's ear. For example, the audio probe signal maybe played back through the loudspeakers 152, 172.

The audio probe signal may be audible or inaudible. In embodiments wherethe audio probe signal is inaudible, the signal may be ultrasonic (e.g.,greater than 20 kHz or in the range 20 kHz to 50 kHz). In embodimentswhere the audio probe signal is audible, and where the trigger event isassociated with a user's desire to interact with the authenticationdevice via speech, the audio probe signal may comprise a prompt to theuser to speak. The prompt may be explicit (e.g., speech from a virtualassistant) or implicit (e.g., a notification tone associated with speechinput).

The audio probe signal may comprise any suitable signal which causes anacoustic response of the user's ear. For example, the audio probe signalmay comprise a chirp of signals at one or more frequencies, white noise,a sound tone, music, speech, etc. In one embodiment, the audio probesignal may be selected or modulated to contain power at frequencieswhich stimulate frequencies in the acoustic response of the user's earwhich are discriminative between different users. Frequencies which maybe discriminative between different users include frequency bandsbetween approximately 1 kHz and approximately 3 kHz; betweenapproximately 5 kHz and approximately 7 kHz; and between approximately10 kHz and approximately 12 kHz. For example, the speech output of avirtual assistant may be modified to contain power at frequencies whichstimulate an acoustic response at those discriminative frequencies.Particular music samples may be chosen, or user-selected music adapted,to contain power at the appropriate frequencies.

In step 206, the authentication device receives a first audio signalcomprising a response of the user's ear to play back of the audio probesignal. As noted above, the response may comprise the audio probe signalas modified by a transfer function associated with the user's ear.Alternatively or additionally, the response may comprise an otoacousticemission from the user's ear. The first audio signal may be generated bya microphone in the vicinity of the user's ear, such as the earmicrophones 154, 174.

In step 208, the authentication device further receives a second audiosignal comprising speech of the user. The speech may comprise one ormore commands or command phrases, e.g., instructions to be carried outby the personal audio device and/or the host device. The second audiosignal may be generated by a voice microphone, such as the microphones156, 176.

In embodiments where the audio probe signal comprises a prompt to theuser to speak, the second audio signal may be received in response tothat prompt.

In order to conserve power, the authentication device may monitor forthe speech only in a limited time window. The time window may begin uponthe audio probe signal ending, for example, and continue for apredetermined period of time. Alternatively, the time window may overlapwith transmission of the audio probe signal. For example, if the probesignal is inaudible, the user will not be aware of it and consequentlymay provide speech (e.g., command speech) before or during the audioprobe signal. Even if the probe signal is audible, a user may not waitfor the audio probe signal before speaking. Consequently, the timewindow may be defined so as to overlap with transmission of the audioprobe signal (e.g., starting before or during transmission of the audioprobe signal) to increase the likelihood that all of the speech isacquired.

Alternatively or additionally, the time window may be defined based onspeech detected in the first audio signal. In this regard, it is notedthat speech detected in the first audio signal is highly likely tocorrespond to speech from the user rather than another person, owing tothe location of the ear microphones close to, or inside the user's ear.That is, speech from the user detected by the ear microphone may havebeen conducted primarily through the user's skull and/or jaw bone andhave a relatively high amplitude, while speech from others is likely tobe attenuated (e.g., owing to a relatively tight acoustic couplingaround the ear canal 112 b).

The time window may therefore be defined based on those times at whichthe first audio signal is substantially correlated with the second audiosignal. Alternatively or additionally, the time window may be definedbased on those times at which speech input is detected in the firstaudio signal.

In step 210, the authentication device performs an ear biometricalgorithm on the first audio signal, and a voice biometric algorithm onthe second audio signal, to authenticate the user as an authorised user.

Each biometric algorithm may comprise the extraction of one or morefeatures from the audio signal, and the comparison of those extractedfeatures to corresponding features in a stored template for anauthorised user. For example, a user will typically undergo a processknown as enrolment, in which biometric data is obtained in a secureenvironment (e.g., once the user has already been authenticated via analternative mechanism, or is deemed authenticated), and features areextracted from that biometric data and stored in a template for thatuser. The user may be required to provide multiple biometric inputs toincrease the reliability of the features extracted for the purposes ofthe template. For example, several samples of ear biometric data may beacquired, or the user may be required to provide multiple spoken inputsas voice biometric data.

In step 210, the relevant features are extracted from the first andsecond audio signals, and compared to the features in those storedtemplates. Thus, one or more features are extracted from the first audiosignal, and compared to corresponding features of the ear biometrictemplate for the authorised user. Similarly, one or more features areextracted from the second audio signal, and compared to correspondingfeatures of the voice biometric template for the authorised user.

One or more biometric scores may be generated, indicative of thelikelihood that the user (i.e., the user providing the biometric input)is the authorised user. For example, the score may be based on themathematical distance (e.g., the cosine vector similarity or any othersuitable comparison algorithm) between the obtained features and thestored features. The one or more biometric scores may then be comparedto one or more threshold values in order to decide whether the usershould be authenticated as the authorised user or not.

The outputs of the voice and ear biometric algorithms may be combined orfused in order to authenticate the user. Various methods of biometricfusion are known in the art, and the present disclosure is not limitedin that respect. For example, separate biometric scores may be generatedfor the ear biometric algorithm and the voice biometric algorithm, andthese biometric scores compared to separate threshold values in order togenerate separate biometric results. These results may then be fused togenerate an overall authentication decision or result (result-levelfusion). For example, the user may be authenticated as the authoriseduser only if both ear and voice biometric results are positive.Alternatively, the separate biometric scores may be combined to generatean overall score, with this overall score then being compared to athreshold value (score-level fusion).

In embodiments where the trigger event comprises a trigger phraseuttered by the user (e.g., a predetermined phrase or word, such as “HeySiri”, “OK Google”, etc.), a voice biometric algorithm may additionallybe performed on features extracted from that trigger phrase, and theoverall authentication decision or result based additionally on thatvoice biometric algorithm.

For example, the voice biometric algorithm may be performed on thepredetermined phrase to obtain a first voice biometric score, and alsoon the command speech (e.g. from the second audio signal) to obtain asecond voice biometric score. The first and second voice biometricscores may be fused with the ear biometric score to obtain an overallbiometric score which can be compared to one or more thresholds toobtain an overall biometric result. Alternatively, as noted above,separate biometric results may be obtained for each biometric process(e.g., based on the first and second voice biometric scores and the earbiometric score) and the results fused to obtain an overall biometricresult.

In step 212, the user is authenticated as the authorised user, or deniedauthentication, based on the ear and voice biometric algorithmsperformed in step 210.

FIG. 3 is a flowchart of a method according to further embodiments ofthe disclosure. Again, the method may be performed by an authenticationdevice which is arranged exclusively within a personal audio device,exclusively within a host device coupled to that personal audio device,or which is distributed between the host device and the personal audiodevice.

In step 300, the authentication device monitors for an event whichtriggers the authentication process (hereinafter, “trigger event”).Various events are contemplated as trigger events according toembodiments of the disclosure.

In one embodiment, the trigger event is indicative of a physicalinteraction with the authentication device. The trigger event mayalternatively or additionally be indicative of a user's desire tointeract with the personal audio device using speech. For example, thetrigger event may be associated with activation of a virtual assistant,e.g., Siri, Cortana, Alexa (all ®), etc.

The trigger event may comprise actuation of a physical or virtual buttonon the personal audio device. Personal audio devices often have suchbuttons in order to send control signals to the personal audio deviceand/or a host device. Different control signals may be generated basedon the type of button actuation (e.g., a short or long press) or on asequence of multiple button actuations (e.g., a chain of two or threebutton presses in sequence). The button may physically move in responseto the user interaction (e.g., a physical button), or comprise acapacitive or ultrasonic sensor (e.g., a virtual button). In anotherexample, a personal audio device may detect finger taps or other userinteractions with the device via a microphone (such as the earmicrophones 154, 174 and/or the voice microphones 156, 176). Pulses ofaudio detected by the microphone may be determined as being indicativeof a tap of the user's fingers on the microphone. In this way, themicrophone itself functions as a button. Trigger events in which abutton is actuated (or its functional equivalent) consume small amountsof power.

In step 302, it is determined whether a trigger event has been detected.If no trigger event has been detected, the method returns to step 300and the authentication device continues to monitor for a trigger event.If a trigger event is detected, the authentication process is initiatedand the method proceeds to step 304.

In step 304, the authentication device generates an audio probe signalto be played through an audio transducer of the personal audio device inthe vicinity of the user's ear. For example, the audio probe signal maybe played back through the loudspeakers 152, 172.

The audio probe signal is audible, and may comprise a prompt to the userto speak. The prompt may be explicit (e.g., speech from a virtualassistant) or implicit (e.g., a notification tone associated with speechinput).

The audio probe signal may comprise any suitable signal which causes anacoustic response of the user's ear. For example, the audio probe signalmay comprise a chirp of signals at one or more frequencies, white noise,a sound tone, music, speech, etc. In one embodiment, the audio probesignal may be selected or modulated to contain power at frequencieswhich stimulate frequencies in the acoustic response of the user's earwhich are discriminative between different users. Frequencies which maybe discriminative between different users include frequency bandsbetween approximately 1 kHz and approximately 3 kHz; betweenapproximately 5 kHz and approximately 7 kHz; and between approximately10 kHz and approximately 12 kHz. For example, the speech output of avirtual assistant may be modified to contain power at frequencies whichstimulate an acoustic response at those discriminative frequencies.Particular music samples may be chosen, or user-selected music adapted,to contain power at the appropriate frequencies.

In step 306, the authentication device receives a first audio signalcomprising a response of the user's ear to play back of the audio probesignal. As noted above, the response may comprise the audio probe signalas modified by a transfer function associated with the user's ear.Alternatively or additionally, the response may comprise an otoacousticemission from the user's ear. The first audio signal may be generated bya microphone in the vicinity of the user's ear, such as the earmicrophones 154, 174.

In step 308, the authentication device performs an ear biometricalgorithm on the first audio signal. Thus, one or more features areextracted from the first audio signal, and compared to correspondingfeatures of an ear biometric template for an authorised user (or thetemplates for multiple authorised users if they exist). An ear biometricscore is generated, indicative of the likelihood that the user (i.e.,the user providing the ear biometric input) is an authorised user, basedon the ear biometric algorithm. For example, the score may be based onthe mathematical distance (e.g., the cosine vector similarity or anyother suitable comparison algorithm) between the obtained features andthe stored features.

In step 310, and in parallel to steps 306 and 308 in the illustratedembodiment, the authentication device further receives a second audiosignal comprising speech of the user in response to the prompt containedin the audio probe signal. The speech may comprise one or more commandsor command phrases, e.g., instructions to be carried out by the personalaudio device and/or the host device. The second audio signal may begenerated by a voice microphone, such as the microphones 156, 176.

In order to conserve power, the authentication device may monitor forthe speech only in a limited time window. The time window may begin uponthe audio probe signal ending, for example, and continue for apredetermined period of time.

Alternatively or additionally, the time window may be defined based onspeech detected in the first audio signal. In this regard, it is notedthat speech detected in the first audio signal is highly likely tocorrespond to speech from the user rather than another person, owing tothe location of the ear microphones close to, or inside the user's ear.That is, speech from the user detected by the ear microphone may havebeen conducted primarily through the user's skull and/or jaw bone andhave a relatively high amplitude, while speech from others is likely tobe attenuated. The time window may therefore be defined based on thosetimes at which the first audio signal is substantially correlated withthe second audio signal. Alternatively or additionally, the time windowmay be defined based on those times at which speech input is detected inthe first audio signal.

In step 312, the authentication device performs a voice biometricalgorithm on the second audio signal. Thus, one or more features areextracted from the second audio signal, and compared to correspondingfeatures of the voice biometric template for the authorised user (ormultiple voice biometric templates for multiple authorised users if theyexist).

In step 314, the outputs of the voice and ear biometric algorithms arecombined or fused in order to authenticate the user. In the illustratedembodiment, result-level fusion is utilized to fuse the results of theear and voice biometric algorithms, i.e., the ear and voice biometricscores are compared to separate thresholds to generate correspondingresults, and the results are combined. Alternatively, the separatebiometric scores may be combined to generate an overall score, with thisoverall score then being compared to a threshold value (score-levelfusion).

In step 316, it is determined whether the user was authenticated as aresult of the combined voice and ear biometric algorithms. If theauthentication is positive, the method proceeds to step 318, in whichthe command spoken by the user in the second audio signal is executed.If the authentication is negative, the method proceeds to step 320 inwhich the command spoken by the user is denied or not executed. In thisregard, speech recognition may be performed on the second audio signal(e.g., the gated parts of the second audio signal) in order to determinethe semantic meaning of the command speech. Speech recognition may beperformed locally (e.g., in the host device or the personal audio deviceif they have sufficient processing capability), or remotely in a speechrecognition service. In the latter case, the second audio signal may betransmitted to the speech recognition service to be processed.

FIG. 4 shows a schematic diagram of an authentication system 400according to embodiments of the disclosure. The authentication system400 comprises an authentication device 402 or processing circuitry(which may be implemented on one or more integrated circuits), a memory404, and one or more input and output devices described below. As notedabove, the authentication device 402 may be provided exclusively withina personal audio device, exclusively within a host device coupled to thepersonal audio device, or distributed between the personal audio deviceand the host device. The memory 404 may similarly be provided within thepersonal audio device, within the host device, or distributed betweenthe personal audio device and the host device.

The system 400 comprises a loudspeaker 406, which may be a microspeaker.The loudspeaker 406 may be arranged within the personal audio device,such that it is located next to a user's ear during use. For example,the loudspeaker 406 may correspond to either of the loudspeakers 152,172 described above with respect to FIGS. 1a and 1 b.

The system 400 further comprises an ear microphone 408. The earmicrophone 408 may be arranged within the personal audio device, suchthat it is located next to a user's ear during use. For example, the earmicrophone 408 may correspond to either of the microphones 154, 174described above with respect to FIGS. 1a and 1 b.

The system 400 further comprises a voice microphone 410. The voicemicrophone 410 may be arranged within the personal audio device, suchthat it is located next to a user's mouth during use. For example, thevoice microphone 410 may correspond to either of the microphones 156,176 described above with respect to FIGS. 1a and 1 b.

The device 402 comprises a control module 412 which is operative toreceive or detect a trigger event, e.g., as described above with respectto steps 200 and/or 300. Responsive to detection of the trigger event,the control module 412 generates an audio probe signal to be played backto the user via the loudspeaker 406.

The audio probe signal may be audible or inaudible. In embodiments wherethe audio probe signal is inaudible, the signal may be ultrasonic (e.g.,greater than 20 kHz or in the range 20 kHz to 50 kHz). In embodimentswhere the audio probe signal is audible, and where the trigger event isassociated with a user's desire to interact with the authenticationdevice via speech, the audio probe signal may comprise a prompt to theuser to speak. The prompt may be explicit (e.g., speech from a virtualassistant) or implicit (e.g., a notification tone associated with speechinput).

The audio probe signal may comprise any suitable signal which causes anacoustic response of the user's ear. For example, the audio probe signalmay comprise a chirp of signals at one or more frequencies, white noise,a sound tone, music, speech, etc. In one embodiment, the audio probesignal may be selected or modulated to contain power at frequencieswhich stimulate frequencies in the acoustic response of the user's earwhich are discriminative between different users. Frequencies which maybe discriminative between different users include frequency bandsbetween approximately 1 kHz and approximately 3 kHz; betweenapproximately 5 kHz and approximately 7 kHz; and between approximately10 kHz and approximately 12 kHz. For example, the speech output of avirtual assistant may be modified to contain power at frequencies whichstimulate an acoustic response at those discriminative frequencies.Particular music samples may be chosen, or user-selected music adapted,to contain power at the appropriate frequencies.

The ear microphone 408 detects the acoustic response of the user's ear,and generates a first audio signal. The first audio signal is detectedby the microphone 408 in the time domain. However, the featuresextracted for the purposes of the biometric process may be in thefrequency domain (in that it is the frequency response of the user's earwhich is characteristic). The device 402 therefore comprises a Fouriertransform module 414, which converts the first audio signal to thefrequency domain. For example, the Fourier transform module 414 mayimplement a fast Fourier transform (FFT). In some examples the biometricprocess may not be in the frequency domain, so the Fourier transformmodule may be omitted.

The output of the Fourier transform module 414 is provided to abiometric authentication module 416, which is configured to perform anear biometric algorithm on the signal, e.g., as described above withrespect to steps 210 and 308. Thus the biometric authentication module416 extracts one or more features from the first audio signal andcompares those features to a stored ear template 420 for an authoriseduser (e.g., an “ear print”), for example as stored in the memory 404.

In some embodiments the biometric authentication module 416 may bedesigned to extract features with foreknowledge of the nature of theaudio probe signal, for example knowing the spectrum of the audio probesignal, so that the response or transfer function may be appropriatelynormalised. In other embodiments the Fourier transform module 414 maycomprise a second input to monitor the audio probe signal (e.g. playbackmusic) and hence provide the biometric authentication module 416 withinformation about the audio probe signal or its spectrum so that thebiometric authentication module may calculate the transfer function fromthe audio probe signal to the received acoustic waveform, from which itmay derive the desired feature parameters.

The voice microphone 410 generates a second audio signal comprisingspeech of the user (e.g., in response to a prompt in the audio probesignal). The second audio signal is also provided to the biometricauthentication module 416, which is configured to perform a voicebiometric algorithm on the signal, e.g., as described above with respectto steps 210 and 312. Thus the biometric authentication module 416extracts one or more features from the second audio signal and comparesthose features to a stored voice template 422 for an authorised user(e.g., a “voice print”), for example as stored in the memory 404. Asnoted above, the biometric authentication module 416 may additionallyperform a voice biometric algorithm on a trigger phrase or word utteredby the user (e.g., and detected as a trigger event to commenceauthentication).

As noted above, in some embodiments the second audio signal is gated,and thus in the illustrated embodiment the authentication device 402further comprises a gating module 418 which is operative to receive thesecond audio signal from the voice microphone 410, and to provide agated signal to the biometric authentication module 416. The gating maybe such that the biometric algorithm is performed only on the secondaudio signal in a limited time window. The time window may begin uponthe audio probe signal ending, for example, and continue for apredetermined period of time. In such embodiments, the control module412 may provide a gating signal to the gating module 418 indicating whenthe audio probe signal has ended.

Alternatively or additionally, the time window may be defined based onspeech detected in the first audio signal. Thus, in the illustratedembodiment, the first audio signal is also provided to the gating module418. The time window may therefore be defined based on those times atwhich the first audio signal is substantially correlated with the secondaudio signal. Alternatively or additionally, the time window may bedefined based on those times at which speech input is detected in thefirst audio signal, e.g., using a voice activity detector (notillustrated).

The biometric authentication module 416 is operative to authenticate theuser as an authorised user based on the ear biometric algorithm and thevoice biometric algorithm. An overall biometric authentication resultmay be output from the biometric authentication module 416 to, forexample, the control module 412 for further processing (e.g., performingor denying a requested task).

Thus embodiments of the present disclosure provide a convenientmechanism for authenticating a user as an authorised user based on earand voice biometrics.

Embodiments described above have focussed on an implementation in whichear biometrics are performed on signals detected in a single ear. Itwill be appreciated by those skilled in the art that the embodiments maystraightforwardly be adapted to take into consideration biometric dataobtained from both ears of a user. Thus, where the description abovediscloses acquiring data from an ear, data may similarly be acquiredfrom two ears. Biometric algorithms may similarly be performed on datafrom both ears, and this may be combined as described above, i.e.separate biometric authentication scores combined to form a combinedscore on which an overall decision is determined, or separate biometricauthentication decisions which are then combined to determine an overalldecision.

Embodiments may be implemented in an electronic, portable and/or batterypowered host device such as a smartphone, an audio player, a mobile orcellular phone, or a handset. Embodiments may be implemented on one ormore integrated circuits provided within such a host device. Embodimentsmay be implemented in a personal audio device configurable to provideaudio playback to a single person, such as a smartphone, a mobile orcellular phone, headset, headphones, earphones. Again, embodiments maybe implemented on one or more integrated circuits provided within such apersonal audio device. In yet further alternatives, embodiments may beimplemented in a combination of a host device and a personal audiodevice. For example, embodiments may be implemented in one or moreintegrated circuits provided within the personal audio device, and oneor more integrated circuits provided within the host device.

It should be understood—especially by those having ordinary skill in theart with the benefit of this disclosure—that the various operationsdescribed herein, particularly in connection with the figures, may beimplemented by other circuitry or other hardware components. The orderin which each operation of a given method is performed may be changed,and various elements of the systems illustrated herein may be added,reordered, combined, omitted, modified, etc. It is intended that thisdisclosure embrace all such modifications and changes and, accordingly,the above description should be regarded in an illustrative rather thana restrictive sense.

Similarly, although this disclosure makes reference to specificembodiments, certain modifications and changes can be made to thoseembodiments without departing from the scope and coverage of thisdisclosure. Moreover, any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element.

Further embodiments likewise, with the benefit of this disclosure, willbe apparent to those having ordinary skill in the art, and suchembodiments should be deemed as being encompassed herein.

1. A method for authenticating a user of an electronic device, themethod comprising: responsive to detection of a trigger event indicativeof a user interaction with the electronic device, generating an audioprobe signal to play through an audio transducer of the electronicdevice, the audio probe signal comprising an audible prompt to the userto speak; receiving a first audio signal comprising a response of theuser's ear to the audio probe signal; receiving a second audio signalcomprising bone-conducted speech of the user in response to the audibleprompt to speak; and applying an ear biometric algorithm to the firstaudio signal and a voice biometric algorithm to the second audio signalto authenticate the user as an authorised user.
 2. The method accordingto claim 1, wherein the audio probe signal comprises a prompt to theuser to speak, and wherein the second audio signal is received inresponse to the prompt.
 3. The method according to claim 1, wherein theear biometric algorithm comprises generation of an ear biometric scorebased on the comparison, and voice biometric algorithm comprisesgeneration of a voice biometric score based on the comparison.
 4. Themethod according to claim 3, wherein the ear biometric score and thevoice biometric score are fused to generate a combined biometric score,and wherein the combined biometric score is compared to one or morethreshold values to generate a combined biometric result.
 5. The methodaccording to claim 3, wherein the ear biometric score is compared to afirst threshold value to generate an ear biometric result, wherein thevoice biometric score is compared to a second threshold value togenerate a voice biometric result, and wherein the ear biometric resultis combined with voice biometric result to generate a combined biometricresult.
 6. An authentication device for authenticating a user of anelectronic device, the authentication device comprising: an audio signalgeneration module for generating, responsive to detection of a triggerevent indicative of a user interaction with the electronic device, anaudio probe signal to play through an audio transducer of the electronicdevice, the audio probe signal comprising an audible prompt to the userto speak; one or more inputs for receiving a first audio signalcomprising a response of the user's ear to the audio probe signal, and asecond audio signal comprising bone-conducted speech of the user inresponse to the audible prompt to speak; and a biometric authenticationmodule for utilizing an ear biometric algorithm on the first audiosignal and a voice biometric algorithm on the second audio signal toauthenticate the user as an authorised user.
 7. The authenticationdevice according to claim 6, wherein the audio probe signal comprises aprompt to the user to speak, and wherein the second audio signal isreceived in response to the prompt.
 8. The authentication deviceaccording to claim 6, wherein the ear biometric algorithm comprisesgeneration of an ear biometric score based on the comparison, and thevoice biometric algorithm comprises generation of a voice biometricscore based on the comparison.
 9. The authentication device according toclaim 8, wherein the ear biometric score and the voice biometric scoreare fused to generate a combined biometric score, and wherein thecombined biometric score is compared to one or more threshold values togenerate a combined biometric result.
 10. The authentication deviceaccording to claim 8, wherein the ear biometric score is compared to afirst threshold value to generate an ear biometric result, wherein thevoice biometric score is compared to a second threshold value togenerate a voice biometric result, and wherein the ear biometric resultis combined with voice biometric result to generate a combined biometricresult.
 11. The authentication device according to claim 8, wherein theear biometric score is generated based on a comparison between one ormore features extracted from the first audio signal and correspondingfeatures of an ear biometric template for the authorised user.
 12. Theauthentication device according to claim 8, wherein the voice biometricscore is generated based on a comparison between one or more featuresextracted from the second audio signal and corresponding features of avoice biometric template for the authorised user.
 13. The authenticationdevice according to claim 6, further comprising a gating moduleconfigured to monitor the second audio signal for the speech of the userin a time window.
 14. The authentication device according to claim 13,wherein the time window is defined in dependence on a gating signalcorresponding to detection of bone-conducted speech in the first audiosignal.
 15. The authentication device according to claim 6, wherein theaudio probe signal is modulated to stimulate the response of the user'sear at one or more frequencies which are discriminative betweendifferent users.
 16. The authentication device according to claim 6,wherein the response of the user's ear comprises one or more of afrequency response of the user's ear canal and an oto-acoustic emissionof the user's ear.
 17. The authentication device according to claim 6,wherein the trigger event comprises a spoken predetermined keyword bythe user.
 18. The authentication device according to claim 6, whereinthe trigger event comprises a physical interaction by the user with theelectronic device.
 19. The authentication device according to claim 6,wherein the speech of the user in response to the prompt comprises acommand for execution by the electronic device.
 20. An electronic devicecomprising the authentication device according to claim 6.